Automatically controlling the operation mode of data circuit terminating equipment in a communication system

ABSTRACT

The operation modes of a plurality of modems in a communication system are matched with each other for connection of digital terminals to an analog telephone line on both the calling and answering sides of the analog telephone line. For example, operation modes of modems on both sides of the analog telephone line can automatically be matched with each other by transferring a mode instructing signal with DTMF, using multi-frequency DTMF symbols for a select signal employed in the telephone line, between digital terminals connected to both ends of the telephone line. More specifically, even in the case of the calling and answering sides being in different initial operation modes, the different operation modes are matched by setting a desired operation mode on the calling side and generating an off-hook signal on the answering side in response to a calling signal, followed by (1) transmitting an operation mode instructing signal in the form of a code with DTMF from the calling side to the answering side, setting the instructed operation mode on the answering side and returning if it can be set on that side, and then returning an answer tone to the calling side for completing the mode matching; or when the operation mode instructed from the calling side cannot be set on the answering side, transmitting an operable mode in the form of a code with DTMF from the answering side to the calling side, and transmitting again the code corresponding to that mode from the calling side to the answering side if that mode can be set on the calling side, thereby matching operation modes of both the calling and answering sides, or (2) transmitting an operation mode instructing signal in the form of a code with DTMF from the answering side to the calling side, and then carrying out a procedure similar to above (1).

TECHNICAL FIELD

The present invention relates to a method of matching operation modes(i.e., operation forms determined by setting of a communication speed, asynchronizing mode, etc.), of data circuit terminating equipment(hereinafter called DCE) such as modems (modulators/demodulators) forconnection of a terminal to a communications network on both the callingand answering sides of the communications network.

BACKGROUND OF THE INVENTION

Data communication using digital terminals connected to one another viaanalog telephone lines has become more prevalent, and modems forperforming conversion of analog signals and digital signals from one tothe other or vice versa between the digital terminals and the analogtelephone lines have been used widely. More specifically, as shown inFIG. 1, a modem DCE has functions of receiving data in the form of adigital signal from a terminal DTE, modulating the input data with apredetermined modulation technique, and outputting an analog signal tothe line side, while it also has functions of demodulating an analogsignal sent from the opposite side via the line with a predetermineddemodulation technique and outputting a demodulated digital signal tothe terminal connected to the other end thereof. Thus, DTE1 and DTE2 onboth the sides can perform data transfer simultaneously or alternatelydependent on communication modes. There are various communication modesas follows:

(1) Full duplex . . . capable of inputting and outputting datasimultaneously

Half duplex . . . inputting and outputting data alternately (only eitherone of inputting and outputting is possible at the same time)

(2) Modulation technique

frequency modulation (FSK)

phase modulation (PSK)

quadrature modulation (QAM);

(3) Communication speed

300 bps (bps: number of transferred bits per second)

1200 bps

2400 bps

4800 bps

7200 bps

9600 bps.

(4) Data form

synchronous

asynchronous.

Various modes are created by diverse combinations of the above items(1), (2), (3) and (4). Thus, data transmission has variety in signalformats and transmission formats. To make matching with those differentformats, some modems are equipped with various operation modes adaptableto the different formats. Further, as transmission standards, there arespecified Recommendations from Consultative Committee of InternationalTelegraph and Telephone (CCITT) V.21, V.22, V22bis, V.23, V.26bis,V.27ter, V.29, etc.

For carrying out digital communication via telephone lines, it isessential to match operation modes of modems installed on both thecalling and answering sides of a communication system.

A conventional mode matching method has been practiced by (a) manuallysetting a modem at the other party in advance, (b) setting the modemduring the sequence for connection, or (c) replacing the modem withanother one as required. However, such a conventional method requiresthe intricate process to make setting for matching of the modems afterexchanging information related to connection conditions between thecalling and answering sides prior to connection of a line, and toreplace the modem itself with a new one when the setting cannot becompleted. Another disadvantage is in that it is difficult for theconventional method to be adaptable for many kinds of operation modesand, even if possible, troublesome operation of shifting a multiplicityof switches is necessitated.

Another conventional method is known which gives an instruction from aterminal to a modem for changing an operation mode of the modem. In thismethod, however, because a command mode and a data mode arediscriminated from each other, shifting from an asynchronous mode to asynchronous mode may become intricate, and shifting from the commandmode to the data mode or from the data mode to the command mode maycause an adverse effect on communication which cannot be disregarded.Another disadvantage of this type modem is in that operation modes couldnot be matched with each other unless the operation of the modem at theother party is known. Accordingly, there has been a desire for a methodcapable of matching modem operation modes regardless of the operationmode of the opposite modem.

The present invention is to improve the disadvantages as mentionedabove, and to provide a method by which operation modes of modems at thetransmit and receive ends of a transmission line is automaticallymatched upon a control command from a terminal. This eliminatesintricacy as encountered in the prior art shifting process.

DISCLOSURE OF THE INVENTION

To solve the foregoing problem, the present invention is, first, toprovide a mode matching method that when communication is performed in asynchronous mode, a digital terminal connected to one end of acommunications network is made operable, the terminal has means forinstructing an operation mode of a DCE for the other party to theone-end DCE upon a control command, the operation mode being stored inadvance, and the one-end DCE analyzes the control command to selectoperation mode reference data for setting the operation mode of theone-end DCE to a predetermined mode.

Secondly, the present invention is to provide a mode matching methodthat DCE's in different operation modes are connected one to either endof communications network, and the operation modes of both the DCE's canautomatically be matched with each other by transferring a modeinstructing signal with DTMF, using multi-frequency DTMF symbols for aselect signal employed in the communications network, between digitalterminals connected to the respective DCE's. More specifically, even inthe case of the calling and answering sides being in different initialoperation modes, a desired operation mode is set on the calling sideupon start-up actuation of the calling side terminal and, after a hookis taken off on the answering side in response to a calling signal, thecalling side transmits an operation mode instructing signal in the formof a code with DTMF to the answering side. The answering side sets theinstructed operation mode if it can be set on that side, and thenreturns an answer tone to the calling side for completing the modematching. If the operation mode instructed from the calling side cannotbe set on the answering side, the answering side transmits an operablemode in the form of a code with DTMF to the calling side. If that modecan be set on the calling side, the code corresponding to that mode istransmitted again from the calling side to the answering side formatching operation modes of both the calling and answering sides.

Thirdly, the present invention is to provide a mode matching methodwhich starts transmission of the operation mode instructing signal fromthe answering side, as a modification of the above second invention.More specifically, even in the case of the calling and answering sidesbeing in different initial operation modes, a desired operation mode isset on the answering side upon actuation of the answering side terminal,and the answering side transmits an operation mode instructing signal inthe form of a code with DTMF to the calling side. The calling side setsthe instructed operation mode if it can be set on that side, and thenreturns an answer tone to the answering side for completing the modematching. If the operation mode instructed from the answering sidecannot be set on the calling side, the calling side transmits anoperable mode in the form of a code with DTMF to the answering side. Ifthat mode can be set on the answering side, the code corresponding tothat mode is transmitted again from the answering side to the callingside for matching operation modes of both the calling and answeringsides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an installation example of modems in the case of utilizinga public telephone line;

FIG. 2 is an explanatory view of a system emboying a matching method ofthe present invention;

FIG. 3 is a block diagram showing the configuration of hardware of aterminal and a modem for implementing the method of the presentinvention;

FIG. 4 is a functional block diagram of the modem;

FIG. 5 is a functional block diagram of the terminal;

FIG. 6 is a chart showing the communication procedure between theterminal and the modem;

FIGS. 7 and 8 are charts showing the communication procedures of othermethods of the present invention;

FIG. 9 is a flowchart for explaining other methods of the presentinvention shown in FIGS. 7 and 8;

FIG. 10 is one example of multi-frequency DTMF symbols for a selectsignal employed in the telephone line;

FIGS. 11 and 12 are charts showing the communication procedures of stillother methods of the present invention; and

FIG. 13 is a flowchart for explaining the still other methods of thepresent invention shown in FIGS. 11 and 12.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 2 shows an outline of a system used for employing a first method ofthe present invention. Designated by reference numeral 10 is a station 1comprising a digital terminal DTE1 and modem DCE1 which are bothconnected to one end of a telephone line 100 and operated in anoperation mode 1. 20, 30 and 40 are stations 2, 3, 4 all connected tothe other end of the telephone line 100 including a branch-exchange,comprising the same equipment as those of the station 1, and operated inoperation modes 2, 3 and 4, respectively.

In FIG. 3, a terminal 31 comprises a microprocessor MPU, a memory MEM, aclock CLOCK, a timer TIMER, a hard disk DK, a disk controller DKC, linecontroller LINC, a serial/parallel interface converter SIO, and a powersupply POW. A modem 32 also comprises a MPU, CLOCK, SIO, MEM and POW aswith the terminal 31. In addition to those, the modem 32 includes adigital signal processor DSP, an analog/digital converter AIC and atelephone line network control unit NCU. The terminal 31 and the modem32 are connected to each other via the respective SIO's.

Functions of various components of the modem DCE will now be described.

SIO (Serial Input Output)

The SIO converts parallel data from the MPU to serial data foroutputting the serial data to the DTE, and converts serial data from theDTE to parallel data for outputting the parallel data to the MPU.

MPU (Micro Processing Unit)

The MPU controls operation of the modem and performs management of adata flow. This is the center of modem control including dialogue onstatus with the DTE by the use of commands and indications, instructionto modulator/demodulator, control of the NCU, control of input andoutput of data, judgement and control of the modem operation mode, etc.

MEM1 and MEM2 (Memory)

These memories are connected to the MPU and the DSP, respectively, andstore data and programs related to operation precedures of the MPU andthe DSP.

DSP (Digital Signal Processor)

The DSP receives data from the DTE via the SIO and the MPU, modulatesthe received data and outputs the modulated data to the AIC. The AICconverts the data into an analog signal and outputs it to the telephoneline via the NCU. On the contrary, an analog signal from the telephoneline via the NCU is converted by the AIC to a digital signal which isthen input to the DSP. The DSP demodulates the digital signal andoutputs it to the MPU. The resulting data is output to the SIO via theDTE.

AIC (Analog Interface Circuit)

The AIC converts the digital signal from the DSP to an analog signal andoutputs it to the NCU, while it converts the analog signal from the NCUto a digital signal and outputs it to the DSP.

NCU (Network Control Unit)

The NCU is to connect the modem and the telephone line and control ofissuance and arrival of a call.

FIG. 4 is a block diagram for explaining a function of the modem DCE1. Acontrol command from the terminal 31 and an information signal to theterminal 31 are transferred via a terminal interface circuit 33 of themodem 32. A modulation/demodulation circuit 35 includes an operationmode reference data area 351, and a command analyzing and operation modesetting circuit 34 is provided between the modulation/demodulationcircuit 35 and the terminal interface circuit 33. A control commandinput from the terminal to the circuit 34 via the interface circuit 33is subjected to analysis of the command and, thereafter, the operationmode setting circuit selects the data for a modem operation modecorresponding to the control command, thereby setting an operation modeof the modulation/demodulation circuit 35 to be matched with that at theother party. As with a usual modem, the modem 32 is connected to atelephone line 37 via the NCU 36.

The above process will be explained again with reference to the blockdiagram of the modem shown in FIG. 3.

When the terminal DTE outputs a command determining an operation mode tothe modem, the command is input to the MPU via the SIO. The MPUinterprets the command which has been prescribed in advance, and selectsa corresponding operation mode. In order to operate the modem in theselected operation mode, the MPU informs or notifies that mode to theDSP for mode setting. A manner of setting the DSP to the instructedoperation mode is mainly divided to two kinds of methods. In the firstmethod, all or most of data and information necessary for enabling theDSP to work in the instructed operation mode are read by the MPU out ofthe memory MEM1 associated with the MPU, and then applied to the DSP. Inother words, the necessary data is downloaded from the MPU to the DSP.In the second method, only a code of the operation mode is informed tothe DSP, whereupon the DSP itself reads the data necessary for itselfout of the memory MEM2 associated with the DSP and makes setting byitself so as to establish the operation mode corresponding to that code.In either method, after completion of setting the modem operation modeby the MPU and the DSP, the MPU informs the completion of the operationto the DTE via the SIO.

FIG. 5 is a block diagram for explaining a function of the terminalDTE1. The terminal 31 includes operation mode setting instruction means41 and is connected to the modem 32 via a modem interface circuit 42.

By referring to the above-mentioned drawings, before issuance or arrivalof a call from or to the DTE1 and DCE1, the DTE1 instructs the DCE1 toset an operation mode corresponding to that of any one of the modemsDCE2, DCE3, DCE4 connected to the other end of the telephone line,whereby the operation mode of the DCE1 is changed to be matched withthat of the opposite modem.

The mode control command applied from the terminal is input to the modeminterface circuit connecting the terminal and the modem via the standardinterface specified in CCITT Recommendation V.24. As shown in FIG. 6,the command is analyzed by the command analyzing and operation modesetting circuit 34, and an indication in the form of an answer tonecorresponding to the command (referred to simply as a indicationhereinafter) is output to the terminal. At this time, the operation modesetting circuit sets the data corresponding to the command from terminalinto a memory area referred to as the operation mode reference dataarea. This permits the modem to operate in the operation mode instructedfrom the terminal in accordance with the set data.

EMBODIMENT 2

FIG. 7 is a chart for explaining a method of matching modem using a tonesignal according to a second embodiment of the present invention.Respective operation modes of modems DCE1 and DCE2 installed at both theends of the telephone line are represented by a mode instructing signalDTMF$$ in the form of a combined code of multi-frequency symbols for aselect signal employed in the telephone line (referred to simply as DTMF(Dual-Tone Multi-Frequency) symbols hereinafter). FIG. 10 shows oneexample of the DTMF symbols employed in the present invention. Although$$ is given by a number of 2 digits for convenience of explanation, thisis intended only to be illustrative and any number of digits can insteadbe selected other than two digits.

The modems DCE1 and DEC2 are each a device comprising a modem circuitand a telephone line network control unit NCU combined with each other.The modem circuit can be adapted for a plurality of modes and selectedany one mode through mode setting.

The modem DEC1, DCE2 and digital terminals DTE1, DTE2 used forimplementing the method of the present invention are constructedsimilarly to the above first embodiment and shown in FIG. 3.

In FIG. 7, it is assumed that prior to start of operation, the DTE1, andthe DCE1 on the calling side are in a state of initial operation mode Iand those on the answering side are in a state of initial operation modeII.

When the operation starts, the calling side terminal DTE1 sends anoperation mode I setting signal SMD$$ to the modem DCE1. This $$ isgiven by two DTMF digits corresponding to the mode I. The modem DCE1responds to the operation mode I setting signal SMD$$ immediately afterstart-up on the calling side, and returns a validation signal VAL to theterminal DTE1, whereby an internal line on the calling side between theterminal DTE1 and the modem DCE1 is set to the desired operation mode I.Then, the calling side modem DCE1 sends out a select signal, such asgiven by a format of call request CRNXXXX in accordance with CCITTRecommendation V.25bias, to the telephone line. This signal XXXX is atrain of digits representing a telephone number of the answering side.

The answering side takes off a hook in response to a ringing tone signalRT, following the predetermined procedure such as prescribed in CCITTRecommendation V.25bis. With the typical off-hook procedure, uponarrival of the ringing tone signal RT, a calling indicating signal CI issent from the modem DCE2 to the terminal DTE2, whereupon the terminalDTE2 returns a termianl ready signal ER to the modem DCE2. Upon receiptof the terminal ready signal ER, the modem DCE2 sends a clear-to-sendsignal CS to the terminal DTE2, followed by the off-hook. After elapseof a delay time T2 necessary for the off-hook to be informed to thecalling side, the modem DCE2 sends out an off-hook end signal (a symbolof DTMF"O" in the illustrated example) to the calling side.

On condition that the off-hook has been detected upon arrival of theoff-hook end signal, the calling side sends out a mode I instructingsignal (in the form of code symbols DTMF$$ corresponding to the mode I)to the answering side.

On condition that the mode I instructing signal has arrived immediatelyafter sending the off-hook end signal, a mode I notifying signal REM issent from the modem DCE2 to the terminal DTE2 on the answering side.Also, on condition that the mode I can be set on the answering side, theterminal DTE2 sends a mode I setting signal SMD$$ to the modem DCE2. Themodem DCE2 returns a validation signal VAL to the terminal DTE2, wherebyan internal line on the answering side between the terminal DTE2 and themodem DCE2 is set to the desired operation mode I.

Thus, the modem at the both ends of the telephone line, i.e., on thecalling and answering sides, are automatically matched to the sameoperation mode, i.e., the operation mode I in this case, so that theobject of the present invention is achieved.

Afterward, the answering side sends an answer tone AT to the callingside, whereby a communicable state is established. Specifically,transmit/receive ready signals DR are sent from the modems to theassociated terminals on both the sides for starting communication.

Although the above explanation has been based on timing relation betweentransfer of the mode I instructing signal and the off-hook signal, thepresent invention is not limited to the foregoing example.

Next, a matching method in the case where the answering side has not theoperation mode instructed by the calling side will be described with thereference to FIGS. 8 and 9.

As with the case of FIG. 7, upon receiving the mode I instructing signalDTMF$$ from the calling side, the modem DCE2 on the answering side sendsthe mode I notifying signal REM$$ to the terminal DTE2. In the case ofFIG. 8, however, since the terminal DTE2 has not the operation moderequested by the calling side, a mode II setting signal SMD@@ as arequest for changing to one of operation modes stocked the terminal DTE2is sent to the modem DCE2. The modem DCE2 returns a validation signalVAL to the terminal DTE2 and also sends out a mode II instructing signalDTMF@@ as a change request to the calling side. Based on the fact that asignal from the answering side responding to the mode I instructingsignal DTMF$$ sent out of the calling side immediately before is givenby not the answer tone AT, but the mode II instructing signal DTMF@@,the calling side recognizes the operation mode change request from theanswering side. The modem DCE1 on the calling side then sends a mode IInotifying signal REM@@ to the terminal DTE1.

Correspondingly, the terminal DTE1 applies a mode II setting signalSMD@@ to the modem DCE1.

In response to the setting signal SMD@@, the modem DCE1 returns avalidation signal VAL to the terminal DTE1, whereby the internal linebetween the terminal DTE1 and the modem DCE1 is set to the desiredoperation mode II. After that setting, the modem DCE1 sends out the modeII instructing signal DTMF@@ to the answering side. The answering sidesets the operation mode to the mode II through the same proocedure asthat on the calling side, and then sends out an answer tone AT to thecalling side so that a communicable state is established. Thus, in theexample of FIG. 2, the modems at the both calling and answering sidescan also automatically be matched to the same operation mode II.

EMBODIMENT 3

A third embodiment is the case where the answering side first instructsan operation mode to the calling side.

A matching method in the case where the calling side has the operationmode instructed from the answering side will now be described withreference to FIG. 11.

Modems DCE1 and DCE2 are each a device comprising a modem circuit and atelephone line network control unit NCU combined with each other. Themodem circuit can be adapted for a plurality of modes and select any onemode through mode setting.

The modems DCE1, DCE2 and digital terminals DTE1, DTE2 used forimplementing the method of the present invention are constructedsimilarly to the above first embodiment and shown in FIG. 3.

In FIG. 11, it is assumed that prior to start of operation, the DTE1 andthe DCE1 on the calling side are in a state of initial operation mode Iand those on the answering side are in a state of initial operation modeII.

When the operation starts, the answering side terminal DTE2 sends anoperation mode I setting signal SMD$$ to the modem DCE2. This $$ isgiven by two DTMF digits corresponding to the mode I. The modem DCE2responds to the operation mode I setting signal SMD$$ immediately afterstart-up on the calling side, and returns a validation signal VAL to theterminal DTE2, whereby an internal line on the calling side between theterminal DTE2 and the modem DCE2 is set to the desired operation mode I.Then, the calling side modem DCE1 sends out a select signal, such asgiven by a format of call request CRNXXXX in accordance, with CCITTRecommendation V.25 bis, to the telephone line. This signal XXXX is atrain of digits representing a telephone number of the answering side.

The answering side takes off a hook in response to a ringing tone signalRT, following the predetermined procedure such as prescribed in CCITTRecommendation V. 25 bis. With the typical off-hook procedure, uponarrival of the ringing tone signal RT, a calling indicating signal CI issent from the modem DCE2 to the terminal DTE2, whereupon the terminalDTE2 returns a terminal ready signal ER to the modem DCE2. Upon receiptof the terminal ready signal ER, the modem DCE2 sends a clear-to-sendsignal CS to the terminal DTE2, followed by the off-hook. After elapseof a delay time T2 necessary for the off-hook to be informed to thecalling side, the modem DCE2 sends out an off-hook end signal (a symbolof DTMF"0" in the illustrated example) to the calling side.

The calling side detects the off-hook upon arrival of the off-hook endsignal. The answering side sends out a mode I instructing signal (in theform of code symbols DTMF$$ corresponding to the mode I) to the callingside.

On condition that the mode I instructing signal has arrived afterdetection of the off-hook end signal, a mode I notifying signal REM issent from the modem DCE1 to the terminal DTE1 on the calling side. Also,on condition that the mode I can be set on the calling side, theterminal DTE1 sends a mode I setting signal SMD$$ to the modem DCE1. Themodem DCE1 returns a validation signal VAL to the terminal DTE1, wherebyan internal line on the calling side between the terminal DTE1 and themodem DCE1 is set to the desired operation mode I.

Thus, the modems at the both ends of the telephone line, i.e., on thecalling and answering sides, are automatically matched to the sameoperation mode, i.e., the operation mode I in this case, so that theobject of the present invention is achieved.

Afterward, the answering side sends an answer tone AT to the callingside, whereby a communicable state is established. Specifically,transmit/receive ready signals DR are sent from the modems to theassociated terminals on both the sides for starting communication.

Although the above explanation has been based on timing relation betweentransfer of the mode I instructing signal and the off-hook signal, thepresent invention is not limited to the foregoing example.

Next, a matching method in the case where the calling side has not theoperation mode instructed by the answering side will be described withreference to FIG. 12.

As with the case of FIG. 11, upon receiving the mode I instructingsignal DTMF$$ from the answering side, the modem DCE1 on the callingside sends the mode I notifying signal REM$$ to the terminal DTE1. Inthe case of FIG. 12, however, since the terminal DTE1 has not theoperation mode requested by the answering side, a mode II setting signalSMD@@ as a request for changing to one of operation modes stocked in theterminal DTE1 is sent to the modem DCE1. The modem DCE1 returns avalidation signal VAL to the terminal DTE1 and also sends out a mode IIinstructing signal DTMF@@ as a change request to the answering side.Based on the fact that a signal from the calling side responding to themode I instructing signal DTMF$$ sent out of the answering sideimmediately before is given by the mode II instructing signal DTMF@@,the answering side recognizes the operation mode change request from thecalling side. The modem DCE2 on the answering side then sends a mode IInotifying siganl REM@@ to the terminal DTE2.

Correspondingly, the terminal DTE2 applies a mode II setting signalSMD@@ to the modem DCE2.

In response to the setting signal SMD@@, the modem DCE2 returns avalidation signal VAL to the terminal DTE2, whereby the internal linebetween the terminal DTE2 and the modem DCE2 is set to the desiredoperation mode II. After that setting, the modem DCE2 sends out the modeII instructing signal DTMF@@ to the answering side. The calling sidesets the operation mode to the mode II through the same procedure asthat on the answering side, and the answering side then sends out ananswer tone AT to the calling side so that a communicable state isestablished. Thus, in the example of FIG. 12, the modems at the bothcalling and answering sides can also automatically be matched to thesame operation mode II.

FIG. 13 shows the above-mentioned operating procedures in the form of aflowchart.

With the present invention, since the terminal can select an operationmode and directly set the selected mode to the modem, it becomespossible to (1) eliminate trouble or labor as otherwise needed insetting and changing the operation mode by intricate manual work, and(2) allow communication with various modems having different operationmodes.

What is claimed is:
 1. A method for controlling a communications systemby matching an operation mode of a first data circuit terminatingequipment ("DCE") with an operation mode of at least a second DCE, saidcommunications system including a first terminal coupled to acommunications netwoork via said first DCE, and a second terminalcoupled to said communications network via said second DCE, said firstand second terminals respectively communicating with said first andsecond DCE's in a synchronous mode, wherein said method comprises thesteps of:storing an initial operation mode of said second DCE in amemory of said first terminal; sending from the first terminal to thefirst DCE an operation mode setting command corresponding to saidinitial operation mode before said first terminal issues to or receivesfrom the communications network a call via said first DCE; analyzingwith the gfirst DCE said operation mode setting command; and controllingsaid first DCE to have an operation mode which matches said initialoperation mode of said second DCE in response to a result of saidanalyzing step.
 2. A method for controlling a communications system bymatching an operation mode a first modem with an operation mode of atleast a second modem, said communications system including a firstterminal coupled to an analog telephone line via said first modem, and asecond terminal coupled to said analog telephone line via said secondmodem, said first and second modems respectively communicating with saidfirst and second terminals in a synchronous mode, wherein said methodcomprises the steps of:storing an initial operation mode of said secondmodem in a memory of said first terminal; sending from the firstterminal to the first modem an operation mode setting commandcorresponding to said inital operation mode before said first terminalissues to or receives from the analog telephone line a call via saidfirst modem; analyzing with the first modem said operation mode settingcommand; and controlling said first modem to have an operation modewhich matches said initial operation mode of said second modem inresponse to a result of said analyzing step.
 3. A method for controllinga communications system by matching an operation mode of a first circuitterminating equipment ("DCE") with an operation mode of at least asecond DCE, said communications system including a first terminalequipment ("DTE") coupled to a communications network via said firstDCE, and second DTE coupled to said communications network via saidsecond DCE, wherein said method comprises the steps of:providing saidfirst DCE with a first set of selected operation modes, and providingsaid second DCE with a second set of selected operation modes such thatsaid first and second DCE's can be set to operate in any one said firstand second sets of selected operation modes, respectively; storingoperation mode command signals in said first DTE corresponding to saidfirst set of selected operation modes, and storing in said second DTEoperation mode command signals corresponding to said second set ofselected operation modes; transmitting from said first DTE to said firstDCE one of said operation mode command signals corresponding to saidfirst set of selected operation modes in accordance with a start-upoperation triggered by said first DTE; following receipt by the secondDCE of a ringing tone signal, transmitting said one operation modecommand signal from said first DCE to said second DCE after a connectionhas been completed therebetween via said communications network; if saidone operation mode command signal corresponds to an operation modeincluded in the second set of selected operation modes, setting anoperation mode of said second DCE to the operation mode corresponding tosaid one operation mode command signal; transmitting an answer signalfrom the second DCE to the first DCE; and transmitting atransmission/receipt ready signal from the first and second DCE'srespectively, the first and second DTE's after said match has occurred.4. The method for controlling a comminications system of claim 3,further comprising the steps of:if said one operation mode commandsignal does not correspond to an operation mode included in the secondset of selected operation modes, transmitting from said second DCE tosaid first DCE another operation mode command signal which correspondsto an operation mode in the second set of selected operation modes; ifsaid other operation mode command signal corresponds to an operationmode included in the first set of selected operation modes, setting anoperation mode of said first DCE to the operation mode corresponding tosaid other operation mode command signal; transmitting said otheroperation mode command signal from the first DCE to said second DCE;setting an operation mode of said second DCE to the peration modecorresponding to other operation mode signal received from said firstDCE; transmitting said answer signal from the second DCE to the firstDCE; and transmitting said transmission/receipt ready signal from thefirst and second DCE's to, respectively, the first and second DTE'safter said match has occurred.
 5. A method for controlling acommunications system by matching an operation mode of a first modemwith an operation mode of at least a second modem, said communicationssystem including a first terminal coupled to an analog telephone linevia said first modem, and a second terminal coupled to said analogtelephone line via said second modem, wherein said method comprises thesteps of:providing said first modem with a first set of selectedoperation modes, and providing said second modem with a second set ofselected operation modes such that said first and second modems can beset to operate in any one of said first and second sets of selectedoperation modes, respectively; storing operation mode command signals insaid first terminal corresponding to said first set of selectedoperation modes, and storing in said second terminal operation modecommand signals corresponding to said second set of selected operationmodes, said operation mode command signals being comprised of combinedcodes composed of mulyi-frequency DTMF codes; transmitting from saidfirst terminal to said first modem one of said operation mode commandsignals corresponding to said first set of selected operation modes inaccordance with a start-up operation triggered by said first terminal;following receipt by the second modem of a ringing tone signal,transmitting said one operation mode command signal from said firstmodem to said second modem after a connection has been completedtherebetween via analog telephone line; if said one operation modecommand signal corresponds to an operation mode included in the secondset of selected operation modes, setting an operation mode of saidsecond modem to the operation mode corresponding to said one operationmode command signal; transmitting an answer signal from the second modemto the first modem; and transmitting a transmission/receipt ready signalfrom the first and second modems to, respectively, the first and secondterminals after said match has occurred.
 6. The method for controlling acommunications system of claim 5, further comprising the steps of:ifsaid one operation mode command signal does not correspond to anoperation mode included in the second set of selected operation modes,transmitting from said second modem to said first modem anotheroperation mode command signal which corresponds to an operation modeincluded in the second set of selected operation modes; if said otheroperation mode command signal corresponds to an operation mode includedin the first set of selected operation modes, setting an operation modeof said first modem to the operation mode corresponding to said otheroperation mode command signal; transmitting said other operation modecommand signal from the first modem to said second modem; setting anoperation mode of said second modem to the operation mode correspndingto said other operation mode signal received from said first modem;transmitting said answer signal from the second modem to the firstmodem; and transmitting said transmission/receipt ready signal from thefirst and second modems to, respectively, the first and second terminalsafter said match has occurred.
 7. A method for controlling acommunications system by matching an operation mode of a first datacircuit terminating equipment ("DCE") with an operation mode at least asecond DCE, said communications system including a first terminalequipment ("DTE") coupled to a communications network via said firstDCE, and a second DTE coupled to said communications network via saidsecond DCE, wherein said method comprises the steps off:providing saidfirst DCE with a first set of selected operation modes, and providingsaid second DCE with a second set of selected operation modes such thatsaid first and second DCE's can be set to operate in any one of saidfirst and second sets of selected operation modes, respectively; storingoperation mode command signals in said first DTE corresponding to saidfirst set of selected operation modes, and storing in said second DTEoperation mode command signals corresponding to said second set ofselected operation modes; transmitting from said second DTE to saidsecond DCE one of said operation mode command signals corresponding tosaid first set of selected operation modes in accordance with a start-upoperation triggered by said second DTE; following receipt by the secondDCE of a ringing tone signal, transmitting said one operation modecommand signal from said second DCE to said first DCE after a connectionhas been completed therebetween via said said communications network; ifsaid one operation mode command signal corresponds to an operation modeincluded in the first set of selected operation modes, setting anoperation mode of said first DCE to the operation mode correspondingsaid one operation mode command signal; transmitting an answer signalfrom the second DCE to the first DCE; and transmitting atransmission/receipt ready signal from the first and second DCE's to,respectively, the first and second DTE's after said match has occurred.8. The method for controlling a communications system of claim 7,further comprising the steps of:if said one operation mode commandsignal does not correspond to an operation mode included in the firstset of selected operation modes, transmitting from said first DCE tosaid second DCE another operation mode command signal which correspondsto an operation mode included in the first set of selected operationmodes; if said other operation mode command signal corresponds to anoperation mode included in the second set of selected operation modes,setting an operation mode of said second DCE to the operation modecorresponding to said other operation mode command signal; transmittingsaid other operation mode command signal from the second DCE to saidfirst DCE; setting an operation mode of said first DCE to the operationmode corresponding said other operation mode signal received from saidsecond DCE; transmitting said answer signal from the second DCE to thefirst DCE; and transmitting said transmission/receipt ready signal fromthe first and second DCE's to, respectively, the first and second DTE'safter said match has occurred.
 9. A method for controlling acommunications system by matching an operation mode of a first modemwith an operation mode of at least a second modem, said communicationssystem including a first terminal coupled to an analog telephone linevia said first modem, and a second terminal coupled to said analogtelephone line via said second modem, wherein said method comprises thesteps of:providing said first modem with a first set of selectedoperation modes, and providing said second modem with a second set ofselected operation modes such that said first and second modems can beset to operate in any one of said first and second sets of selectedoperation modes, respectively; storing operation mode command signals insaid first terminal corresponding to said first set of selectedoperation modes, and storing in said second terminal operation modecommand signals corresponding to said second set of selected operationmodes; transmitting from said second terminal to said second modem oneof said operation mode command signals corresponding to said second setof selected operation modes in accordance with a start-up operationtriggered by said second terminal; following receipt by the second modemof a ringing tone signal, transmitting said one operation mode commandsignal from said second modem to said first modem after a connection hasbeen completed therebetween via said analog telephone line; if said oneoperation mode command signal corresponds to an operation mode includedin the first set of selected operation modes, setting an operation modeof said first modem to the operation mode corresponding to said oneoperation mode command signal; transmitting an answer signal from thesecond modem to the first modem; and transmitting a transmission/receiptready signal from the first and second modems to, respectively, thefirst and second terminals after said match has occurred.
 10. The methodfor controlling a communications system of claim 9, further comprisingthe steps of:if said one operation mode command signal does notcorrespond to an operation mode included in the first set of selectedoperation modes, transmitting from said first modem to said second modemanother operation mode command signal which corresponds to an operationmode included in the first set of selected operation modes; if saidother operation mode command signal corresponds to an operation modeincluded in the second set of selected operation modes, setting anoperation mode of said second modem to the operation mode correspondingto said other operation mode command signal; transmitting said otheroperation mode command signal from the second modem to said first modem;setting an operation mode of said first modem to the operation modecorresponding to said other operation mode signal received from saidsecond modem; transmitting said answer signal from the second modem tothe first modem; and transmitting said transmission/receipt ready signalfrom the first and second modems to, respectively, the first and secondterminals after said match has occurred.
 11. A communications system,comprising:a first terminal coupled to a communications network via afirst data circuit terminating equipment ("DCE"); a second terminalcoupled to said communications network via a second DCE; means tocontrol said first and second terminals for respectively communicatingwith said first and second DCE's in a synchronous mode; wherein saidfirst terminal comprisesmeans for storing an initial operation mode ofsaid second DCE; and means for sending from the first terminal to thefirst DCE an operation mode setting command corresponding to saidinitial operation mode before said first terminal issues to or receivesfrom the communications network a call via said first DCE; and whereinsaid first DCE includesmeans for analyzing said operation mode settingcommand; and means for controlling said first DCE to have an operationmode which matches said initial operation mode of said second DCE inresponse to an output of said analyzing means.
 12. A communicationssystem, comprising:a first terminal coupled to an analog telephone linevia a first modem; a second terminal coupled to said analog telephoneline via a second modem; means to control said first and second modemsfor respectively communicating with said first and second terminals in asynchronous mode; wherein said first terminal includesmeans for storingan initial operation mode of said second modem; and means for sendingfrom the first terminal to the first modem an operation mode settingcommand corresponding to said initial operation mode before said firstterminal issues to or receives from the analog telephone line a call viasaid first modem; and wherein said first modem includesmeans foranalyzing said operation mode setting command; and means for controllingsaid first modem to have an operation mode which matches said initialoperation mode of said second modem in response to an output of saidanalyzing means.
 13. A communications system, comprising:a firstterminal equipment ("DTE") coupled to a communications network via afirst data circuit terminating equipment ("DCE"); a second DTE coupledto said communications network via a second DCE; means for providingsaid first DCE with a first set of selected operation modes, and forproviding said second DCE with a second set of selected operation modessuch that said first and second DCE's can be set to operate in any oneof said first and second sets of selected operation modes, respectively;means for storing operation mode command signals in said first DTEcorresponding to said first set of selected operation modes, and meansfor storing in said second DTE operation mode command signalscorresponding to said second set of selected operation modes; means fortransmitting from said first DTE to said first DCE one of said operationmode command signals corresponding to said first set of selectedoperation modes in accordance with a start-up operation triggered bysaid first DTE; means for, following receipt by the second DCE of aringing tone signal, transmitting said one operation mode command signalfrom said first DCE to said second DCE after a connection has beencompleted therebetween via said communications network; means for, ifsaid one operation mode command signal corresponds to an operation modeincluded in the second set of selected operation modes, setting anoperation mode of said second DCE to the operation mode corresponding tosaid one operation mode command signal; means for transmitting an answersignal from the second DCE to the first DCE; and means for transmittinga transmission/receipt ready signal from the first and second DCE's to,respectively, the first and second DTE's after said match has occurred.14. The communications system of claim 13, further comprising:means for,if said one operation mode command signal does not correspond to anoperation mode included in the second set of selected operation modes,transmitting from said second DCE to said first DCE another operationmode command signal which corresponds to an operation mode included inthe second set of selected operation modes; means for, if said otheroperation mode command signal corresponds to an operation mode includedin the first set of selected operation modes, setting an operation modeof said first DCE to the operation mode corresponding to said otheroperation mode command signal; means for transmitting said otheroperation mode command signal from the first DCE to said second DCE;means for setting an operation mode of said second DCE to the operationmode corresponding to said other operation mode signal received fromsaid first DCE; means for transmitting said answer signal from thesecond DCE to the first DCE; and means for transmitting saidtransmission/receipt ready signal from the first and second DCE's to,respectively, the first and second DTE's after said match has occurred.15. A communications system, comprising:a first terminal coupled to ananalog telephone line via a first modem; a second terminal coupled tosaid analog telephone line via a second modem; means for providing saidfirst modem with a first set of selected operation modes, and forproviding said second modem with a second set of selected operationmodes such that said first and second modems can be set to operate inany one of said first and second sets of selected operation modes,respectively; means for storing operation mode command signals in saidfirst terminal corresponding to said first set of selected operationmodes, and means for storing in said second terminal operation modecommand signals corresponding to said second set of selected operationmodes, said operation mode command signals being comprised of combinedcodes composed of multi-frequency DTMF codes; means for transmittingfrom said first terminal to said first modem one of said operation modecommand signals corresponding to said first set of selected operationmodes in accordance with a start-up operation triggered by said firstterminal; means for, following receipt by the second modem of a ringingtone signal, transmitting said one operation mode command signal fromsaid first modem to said second modem after a connection has beencompleted therebetween via said analog telephone line; means for, ifsaid one operation mode command signal corresponds to an operation modeincluded in the second set of selected operation modes, setting anoperation mode of said second modem to the operation mode correspondingto said one operation mode command signal; means for transmitting ananswer signal from the second modem to the first modem; and means fortransmitting a transmission/receipt ready signal from the first andsecond modems to, respectively, the first and second terminals aftersaid match has occurred.
 16. The communications system of claim 15,further comprising:means for, if said one operation mode command signaldoes not correspond to an operation mode included in the second set ofselected operation modes, transmitting from said second modem to saidfirst modem another operation mode command signal which corresponds toan operation mode included in the second set of selected operationmodes; means for, if said other operation mode command signalcorresponds to an operation mode included in the first set of selectedoperation modes, setting an operation mode of said first modem to theoperation mode corresponding to said other operation mode commandsignal; means for transmitting said other operation mode command signalfrom the first modem to said second modem; means for setting anoperation mode of said second modem to the operation mode correspondingto said other operation mode signal received from said first modem;means for transmitting said answer signal from the second modem to thefirst modem; and means for transmitting said transmission/receipt readysignal from the first and second modems to, respectively, the first andsecond terminals after said match has occurred.
 17. A communicationssystem, comprising:a first terminal equipment ("DTE") coupled to acommunications network via a first data circuit terminating equipment("DCE"); a second DTE coupled to said communications network via asecond DCE; means for providing said first DCE with a first set ofselected operation modes, and for providing said second DCE with asecond set of selected operation modes such that said first and secondDCE's can be set to operate in any one of said first and second sets ofselected operation modes, respectively; means for storing operation modecommand signals in said first DTE corresponding to said first set ofselected operation modes, and for means for storing in said second DTEoperation mode command signals corresponding to said second set ofselected operation modes; means for transmitting from said second DTE tosaid second DCE one of said operation mode command signals correspondingto said first set of selected operation modes in accordance with astart-up operation triggered by said second DTE; means for, followingreceipt by the second DCE of a ringing tone signal, transmitting saidone operation mode command signal from said second DCE to said first DCEafter a connection has been completed therebetween via saidcommunications network; means for, if said one operation mode commandsignal corresponds to an operation mode included in the first set ofselected operation modes, setting an operation mode of said first DCE tothe operation mode corresponding to said one operation mode commandsignal; means for transmitting an answer signal from the second DCE tothe first DCE; and means for transmitting a transmission/receipt readysignal from the first and second DCE's to, respectively, the first andsecond DTE's after said match has occurred.
 18. The communicationssystem of claim 17, further comprising:means for, if said one operationmode command signal does not correspond to an operation mode included inthe first set of selected operation modes, transmitting from said firstDCE to said second DCE another operation mode command signal whichcorresponds to an operation mode included in the first set of selectedoperation modes; means for, if said other operation mode command signalcorresponds to an operation mode included in the second set of selectedoperation modes, setting an operation mode of said second DCE to theoperation mode corresponding to said other operation mode commandsignal; means for transmitting said other operation mode command signalfrom the second DCE to said first DCE; means for setting an operationmode of said first DCE to the operation mode corresponding to said otheroperation mode signal received from said second DCE; means fortransmitting said answer signal from the second DCE to the first DCE;and means for transmitting said transmission/receipt ready signal fromthe first and second DCE's to, respectively, the first and second DTE'safter said match has occurred.
 19. A communications system, comprising:afirst terminal coupled to an analog telephone line via a first modem; asecond terminal coupled to said analog telephone line via a secondmodem; means for providing said first modem with a first set of selectedoperation modes, and for providing said second modem with a second setof selected operation modes such that said first and second modems canbe set to operate in any one of said first and second sets of selectedoperation modes, respectively; means for storing operation mode commandsignals in said first terminal corresponding to said first set ofselected operation modes, and means for storing in said second terminaloperation mode command signals corresponding to said second set ofselected operation modes; means for transmitting from said secondterminal to said second modem one of said operation mode command signalscorresponding to said second set of selected operation modes inaccordance with a start-up operation triggered by said second terminal;means for, following receipt by the second modem of a ringing tonesignal, transmitting said one operation mode command signal from saidsecond modem to said first modem after a connection has been completedtherebetween via said analog telephone line; means for, if said oneoperation mode command signal corresponds to an operation mode includedin the first set of selected operation modes, setting an operation modeof said first modem to the operation mode corresponding to said oneoperation mode command signal; means for transmitting an answer signalfrom the second modem to the first modem; and means for transmitting atransmission/receipt ready signal from the first and second modems to,respectively, the first and second terminals after said match hasoccurred.
 20. The communications system of claim 19, furthercomprising:means for, if said one operation mode command signal does notcorrespond to an operation mode included in the first set of selectedoperation modes, transmitting from said first modem to said second modemanother operation mode command signal which correspond to an operationmode included in the first set of selected operation modes; means for,if said other operation mode command signal corresponds to an operationmode included in the second set of selected operation modes, setting anoperation mode of said second modem to the operation mode correspondingto said other operation mode command signal; means for transmitting saidother operation mode command signal from the second modem to said firstmodem; means for setting an operation mode of said first modem to theoperation mode corresponding to said other operation mode signalreceived from said second modem; means for transmitting said answersignal from the second modem to the first modem; and means fortransmitting said transmission/receipt ready signal from the first andsecond modems to, respectively, the first and second terminals aftersaid match has occurred.